soluble in these solvents. Its physical and chemical characters are riven
in Table XLIV.
Castor oil is readily distinguished from other oils by its solubility in
alcohol and its insolubility in mineral oils, by its specific gravity, acetyl
number, viscosity and rotatory power, which are considerably higher than
with other oils. Its viscosity (Engler) at 50° is about 16 (water at 20 = i)
and its rotation in a 20 cm. tube at the ordinary temperature + 8° to + 9°
When prepared recently and in thecold, ic is neutral, but it easily becomes
rancid. Old oils and those extracted in the hot or by solvents are more or
less acid (up to more than 20% of free acids, as oleic acid).
The following tests are usually made:
1. Solubility.—'This serves to show if the oil is pure or not, and is
carried out as follows :
(a) Finkener's test. 10 c.c. of the oil and 50 c.c. of 90% alcohol are
shaken together : if the mixture is turbid and remains so at 20°, the castor
oil is not pure.
(b) Morpurgo's test, i vol. of the oil and 3 vols. of oil of vaseline are
shaken together at 10-15° : after standing, the oil of vaseline separates
with its original volume if the castor oil is pure, but with an increased
volume if extraneous oils are present.
2. Detection of Adulterations.—(a) VARIOUS VEGETABLE OILS.
Castor oil is rarely adulterated with vegetable oils (cottonseed, sesame,
colza, linseed, etc.), which may in any case be easily detected, since they
lower the specific gravity, acetyl number and rotatory power and raise
the saponification number (excepting colza or ravison oil).
(&) CROTON ELLIOTIANUS OIL. Tffis oil does not greatly alter the
properties and is difficult to detect, especially if only in small proportion.
An indication of its presence may, however, be obtained by boiling the
oil with a very concentrated potassium hydroxide solution : on cooling, a
white, soapy mass is obtained with pure castor oil, and a yellow or brown
mass in presence of croton oil (i% or more).1
3. Test for Resinous Substances.—To ascertain if a sample of castor
oil is contaminated with resinous substances or has been extracted in the
hot, the following test, prescribed by the official Italian pharmacopoeia, is
made. 3 c.c. of the oil, 3 c.c. of carbon disulphide and i c.c. of cone,
sulphuric acid are shaken together for some minutes : the mixture should
not turn brown. H
Medicinal castor oil, according to the official Italian pharmacopoeia, should
be extracted by pressure in the cold from husked, peeled seeds ; it should be
clear, almost colourless or yellowish, and not of acrid taste, soluble in 5 parts
of 90% alcohol at 15° and in 2 parts at 25°,'and extremely soluble in absolute
alcohol, ether or glacial acetic acid. Its iodine number should be 80-85, and
its saponification number 180-182, and it should answer to the reaction, described
Detection of croton oil in castor oil (Arch, di farm, sper., 1905,ve of hydroxy-acids)—to be determined by saponifying